44

ENGINEERING  CHEMISTRY

siderable degree of manipulative skill, and can be undertaken only by a
trained chemist. The principles underlying it, however, are those exem-
plified in the use of the Orsat as described above, more elaborate apparatus
being used to obtain a higher degree of accuracy, and the samples collected
and measured over mercury for the same reason. Carbon dioxide, oxygen,
and carbon monoxide are absorbed in the order named and by the use of the
reagents already described. Ethylene if present may be absorbed by bromine.

A portion of the residual gas is
then taken, mixed with an excess
of air or oxygen, and exploded
by an electric spark while con-
tained over mercury in a stout
glass vessel known as an ex-
plosion pipette. The hydrogen
is burned into water, the hydro-
carbons into carbon dioxide and
water. The volume of the
carbon dioxide produced is equal
to the amount of methane, and
from the total shrinkage result-
ing on explosion the hydrogen
i is obtainable by calculation.
Carbon Dioxide Re-
corders.—The absorption of
carbon dioxide by means of
caustic potash, which is used for
its determination in the ordinary
methods of gas analysis, is rapid,
and by the employment of
mechanical arrangements such
absorptions can be carried on
successively and without super-
vision, the percentages of carbon
dioxide in the gas mixture being
Fig. 2.—CO2 Recorder
re-
CO,
recorded on a chart.
corders of this kind now form
part of the necessary equipment of a modern installation for the economical
production of heat by combustion. A single recorder may be arranged to
operate on a battery of boilers, but a more satisfactory practice is to have an
instrument recording the working of each boiler separately. These may be
erected singly or in a group occupying one case, and, beyond the periodical
refilling of the caustic potash holder and attention to the changing of the
records, they require little looking after. From a study of the charts it is
possible to judge the efficiency of the furnace working from hour to hour,
to adjust the draft to what is necessary for perfect combustion, avoiding too
much excess air, to fix the best thickness of fire, and to detect the presence